The invention described herein relates to a method for separating the isotopes of hydrogen, and more specifically to a method wherein the isotopes of hydrogen are separated as a result of isotope preferential or selective photochemical reaction in the liquid phase.
The Candu fission reactor employs natural uranium rather than enriched uranium as its fuel. To do this, however, requires the use of heavy water (D.sub.2 O) as the moderator and coolant. The separation of hydrogen isotopes in quantities sufficient to meet the large amounts of heavy water required constitutes a significant portion of the cost of Candu reactors. At present, most of the heavy water is produced by the Girdler sulfide process, a process which requires large quantities of H.sub.2 S at high pressure. Since H.sub.2 S in quantities larger than a few parts per million is poisonous, the accidental release of this material represents a significant potential health hazard in the use of the Girdler process. Thus, another efficient and economical means of achieving the required hydrogen isotope separation is highly desirable.
Laser-induced separation of hydrogen isotopes is known in the art. To accomplish laser-induced separation of hydrogen isotopes by photochemical techniques requires the following requirements to be met: (1) A chemical compound of hydrogen must be available which has optical absorption features for which the absorption varies rapidly with wavelength and which appear at different wavelengths for different hydrogen isotopes, i.e., there must be a well delineated isotope shift, so that the excitation can be preferentially induced in isotopically distinct molecules of the compound. (2) The excited molecules must then either spontaneously undergo or be induced to undergo some sort of chemical change more rapidly than the unexcited molecules. (3) The product hydrogen compound or molecule which results must possess properties which permit its separation by physical or chemical means from the reactant or feed hydrogen compound. The separated hydrogen-bearing product molecules will then be isotopically enriched. It will be apparent that the degree of enrichment will depend upon the amount of selectivity in the excitation and photochemical reaction steps and the amount of scrambling which occurs before the product hydrogen-bearing molecules are separated from the reactant or feed hydrogen compound. By scrambling is meant any chemical or physical process the effect of which is to exchange isotopes or excitation and which results in a lesser degree of selectivity.
Various methods for the laser-induced photochemical separation of hydrogen isotopes using gaseous feed materials are known in the art. Formaldehyde is known to be quite useful as a feed material in laser-induced hydrogen isotope separation. See, e.g., Jack Marling, "Isotope Separation of Oxygen-17, Oxygen-18, Carbon-13, and Deuterium by Ion Laser Induced Formaldehyde Photopredissociation," J. Chem. Phys. 66, 4200 (1977).
For a separation scheme to be most economical, it is necessary to handle large quantities of the feed material, and it is helpful if the apparatus for handling this material is not too complex. These two facts suggest that economical laser-induced isotope separation is more easily accomplished if the molecular density of the hydrogen-bearing feed material is reasonably high. Moreover, the foregoing requirements must be capable of being met in a practical environment envisioned for a given isotope separation scheme. It will be apparent that for efficient, large-scale isotope separation, this environment will preferably be a flowing one. Finally, the raw or feed materials should be inexpensive and the separation of the products simple.
Heretofore the art has disclosed laser-induced hydrogen isotope separation methods in which the irradiation occurs to a feed material in the gaseous phase. But to meet the foregoing criteria, it would be highly advantageous to perform the irradiation of the feed material when it is in a liquid phase. The published literature does not disclose any method for achieving laser-induced isotope separation using a feed material in the liquid phase.
A basic reason why laser-induced isotope separation methods based on irradiation in the liquid phase have not heretofore been reported is that the spectral features exhibited by compounds in the liquid state or in solution at or near room temperature (300.degree. K.) are considered to be substantially broader than the isotope shift so that condition (1) listed herein cannot be met.